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Publication numberUS4214300 A
Publication typeGrant
Application numberUS 05/906,253
Publication dateJul 22, 1980
Filing dateMay 15, 1978
Priority dateMay 17, 1977
Publication number05906253, 906253, US 4214300 A, US 4214300A, US-A-4214300, US4214300 A, US4214300A
InventorsPaul Barlow, Kenneth R. Jones
Original AssigneeKenneth Robert Jones
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Three term (PID) controllers
US 4214300 A
Abstract
A method and apparatus for adjusting a variable parameter of a dynamic system in response to a signal representative of the system performance so as to optimize system performance with respect to that parameter. A first signal related to system performance is extracted from the dynamic system and is thereafter coupled to a plurality of performance index blocks, each of these blocks for operating on this signal according to a different predetermined characteristic transfer function. The output level from a selected performance index block is periodically sampled and the sampled level is compared with a previously sampled level to provide a positive or negative difference signal. A first pulsed signal is formed wherein pulses and zero levels are respectively representative of the incidence of opposite polarity levels in the difference signal. This first pulsed signal is converted into a second pulsed signal wherein the leading and trailing edges of the pulses correspond to the incidence of adjacent pulses in the first pulsed signal. The zero axis position is shifted in relation to the second pulsed signal to obtain positive and negative signals whose width is representative of the extent to which the variable parameter of the dynamic system must be inreased or decreased. The positive and negative signals are integrated to provide an output signal for adjusting this variable parameter.
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Claims(12)
We claim:
1. An electronic circuit for adjusting a variable parameter of a dynamic system in response to a signal representative of the system performance so as to optimize the system performance with respect to that parameter, the circuit comprising:
(a) means for extracting from the dynamic system a first signal dependent upon the system performance;
(b) a plurality of performance index blocks coupled to said means for extracting so as to receive said first signal each of said blocks for providing a different predetermined characteristic function of said first signal;
(c) switch means coupling said means for extracting to said plurality of performance index blocks for selecting one of said performance index blocks;
(d) means coupled to said performance blocks for periodically sampling and comparing the output level from a selected performance index block with a previously sampled level and for providing a difference signal indicative of whether the result of said comparison is positive or negative;
(e) means coupled to said means for sampling and comparing for providing a first pulsed signal wherein pulses and zero levels are respectively indicative of the incidence of opposite polarity levels in said difference signal;
(f) means coupled to said means for providing a first pulsed signal for converting said first pulsed signal into a second pulsed signal wherein the leading and trailing edges of the pulses correspond to the incidence of adjacent pulses in said first pulsed signal;
(g) means for shifting the zero axis position in relation to said second pulsed signal to obtain positive and negative signals whose width is indicative of the extent to which the parameter to be varied must be increased or decreased; and
(h) integrator means for receiving said positive and negative signals and for providing an output signal for adjusting said parameter.
2. A circuit for controlling a one, two or three term (PID) controller in a closed loop control system for a process, comprising first means for monitoring a predetermined characteristic function of the system error; and second means for automatically adjusting the response characteristic of said controller in response to the value of said characteristic function, said first means comprising:
a unit for injecting a test signal into said closed loop for deriving an error signal therefrom;
a circuit element having a plurality of performance index blocks each of which provides a different predetermined characteristic function; and
switch means coupling said circuit element to said second means for selecting one of said performance index blocks.
3. A circuit as claimed in claim 2 wherein said circuit element has four selectable performance index blocks respectively providing the following predetermined characteristic functions: Mean Square Error; Integral of Squared Error; Integral of Absolute Error; and Integral of Time and Absolute Error.
4. A circuit as claimed in claim 3 wherein said circuit element further includes:
a multiplier unit for receiving and squaring said error signal;
an amplifier for averaging the squared error signal from said multiplier to provide said Mean Square Error function; and
an integrator for integrating said squared error signal to provide said Integral of Squared Error function.
5. A circuit as claimed in claim 4 wherein said circuit element further includes:
a circuit for providing the modulus of the error signal; and
an integrator connected thereto for integrating said error signal modulus to provide said Integral of Absolute Error function.
6. A circuit as claimed in claim 5 wherein said circuit element further includes:
an integrator for receiving and integrating a step signal;
a multiplier unit for multiplying said error signal modulus function with the integral of said step signal; and
a further integrator for integrating the product of said error signal modulus and said integral to provide said Integral of Time and Absolute Error function.
7. A circuit as claimed in claim 2 wherein said second means comprises:
a comparator for comparing predetermined characteristic function values derived from successive test signals;
a complementary memory pair coupling said performance index block to said comparator and operable to sample and hold successive predetermined characteristic function values for comparison with one another; and
third means for generating a correction signal in response to said comparison for adjusting said response characteristic.
8. A circuit as claimed in claim 7 wherein said response characteristic is the gain of at least one channel of said controller.
9. A circuit as claimed in claim 8 wherein said second means is operable for automatically adjusting the gains of three channels of said controller.
10. A circuit as claimed in claim 9 wherein said second means further comprises a time sharing unit for successively and separately adjusting said gains.
11. An electronic circuit for automatically adjusting the response characteristic of a one, two or three term (PID) controller in a closed loop control system in response to a predetermined function of the control system error, the circuit comprising:
(a) means for injecting a test signal into said closed loop for creating a system error;
(b) means for extracting from said control system a first signal in response to said system error;
(c) a plurality of performance index blocks coupled to said first signal each of which blocks provides a different predetermined characteristic function of said first signal corresponding to said system error;
(d) switch means for selecting one of said performance index blocks;
(e) means for periodically sampling the output level from a selected performance index block and for comparing the sampled level with a previously sampled level to provide a difference signal indicative of whether the result of the comparison is positive or negative;
(f) means for providing a first pulsed signal wherein pulses and zero levels are respectively indicative of the incidence of opposite polarily levels in said difference signal;
(g) means for converting said pulsed signal into a second pulsed signal wherein the leading and trailing edges of the pulses of said second pulsed signal correspond to the incidence of adjacent pulses in said first pulsed signal;
(h) means for shifting the zero axis position in relating to said second pulsed signal to obtain positive and negative signals whose width is representative of the extent to which the response characteristic to be varied must be increased or decreased; and
(i) integrator means for receiving said positive and negative signals to provide an output signal for adjusting said response characteristic.
12. A method for adjusting a variable parameter of a dynamic system in response to a signal representative of the system performance so as to optimize the system performance with respect to that parameter, the method comprising the steps of:
(a) extracting from the dynamic system a first signal dependent upon the system performance;
(b) coupling said first signal to a plurality of performance index blocks, each of which blocks provides a different predetermined characteristic function of said first signal;
(c) selecting one of said performance index blocks;
(d) periodically sampling the output level from the selected performance index block and comparing the sampled level with a previously sampled level to provide a difference signal representative of whether the result of the comparison is positive or negative;
(e) forming a first pulsed signal wherein pulses and zero levels are respectively representative of the incidence of opposite polarity levels in said difference signal;
(f) converting said pulsed signal into a second pulsed signal wherein the leading and trailing edges of the pulses correspond to the incidence of adjacent pulses in said first pulsed signal;
(g) shifting the zero axis position in relation to said second pulsed signal to obtain positive and negative signals whose width is representative of the extent to which the parameter to be varied must be increased or decreased; and
(h) integrating said positive and negative signals to provide an output signal for adjusting said parameter.
Description

The present invention relates to one, two or three term (PID) controllers for closed loop, process control systems.

Three term PID controllers are used in control systems to enable such systems to respond to three different functions of the system error, namely a Proportional function, an Integral function and a Differential function. In conventional systems, the response characteristic of the three control channels corresponding to these three functions are arranged to be manually pre-set by a system operator in accordance, inter alia, with the operational characteristics of the process being controlled. However, should these characteristics of the process change with time, either the efficiency of the control becomes lower or further manual adjustments have to be made, probably by trial and error, in order to attempt to regain an optimum operating condition.

In accordance with the present invention, there is provided a method of optimising the operating characteristics of a process which is controlled by a closed loop control system using a three term (PID) controller having three control channels, comprising monitoring a predetermined characteristic function of the system error and automatically adjusting the response characteristic of said controller in dependence on said function value.

The present invention also provides a circuit for controlling a three term (PID) controller in a closed loop control system for a process, comprising first means for monitoring a predetermined characteristic function of the system error and second means for automatically adjusting the response characteristic of said controller in dependence on said function value.

The invention is described further hereinafter, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a block circuit diagram of a closed loop control system which includes a three-term controller having a self-tuning circuit in accordance with the present invention;

FIG. 2 is a block circuit diagram of one embodiment of the self-tuning circuit for the controller of FIG. 1;

FIGS. 3 and 4 are circuit diagrams illustrating one form of time sharing unit;

FIG. 5 is a detailed view of a circuit element of FIG. 2 for establishing the system performance index; and

FIG. 6 is a detailed view of a three term P.I.D. controller of the system of FIG. 2;

The closed loop system of FIG. 1 includes a process 10 which is to be controlled in accordance with a predetermined characteristic. For this purpose an output signal of the process 10, for example from some form of electrical transducer which is responsive to an operational parameter of the process such as temperature, pressure etc., is fed back by way of a line 12 and subtracted in a comparator 14 from an input signal on a line 16 to form a system error signal E on a line 18. The error signal E on line 18 is used as an input control signal for the process 10 by way of a three term (PID) controller 19 which enables the process control to be responsive to the three different functions of the error E, that is the Proportional function, Integral function and Differential function. Each function has an associated channel gain designated by K1, K2 and K3, respectively.

The system as so far described is conventional. Normally in such a system, the channel gains K1, K2 and K3 are set up manually at the start of the process and remain unaltered until such time as a further manual adjustment is made, for example upon the operator realising that a long term variation in the process conditions has occurred which requires the system response to be altered.

In the present system, means are provided for automatically adjusting the various channel gains K1, K2, and K3 of the three term controller to take account of variations, of both a short and long term nature, in the process conditions and to maintain optimum control as defined by a predetermined characteristic function, preferably some function of the system error E, referred to as the performance index and related to the system efficiency. For this purpose, the system includes a self-tuning circuit 20 which is illustrated in more detail in FIGS. 2 and 3.

In the circuit 20, the system error signal E is applied as an input signal to a circuit element 22 where a performance index is established. As indicated in FIG. 2, the performance index can be pre-selected from a plurality of predetermined functions of the system error E of which there are four in this embodiment, namely Mean Square Error (MSE), Integral of Squared Error (ISE), Integral of Absolute Error (IAE) and Integral of Time and Absolute Error (ITAE), these being examples only of the type of function which may be utilised. The choice of the particular function used to determine the performance index is made by the operator in accordance with the characteristics of the particular process 10 which is to be controlled. In general, the performance index characteristic corresponds to a simple or complex curve of the type in which x is a double value function of y and which has a stationary value in the range of interest, i.e. it defines a peak or a trough on the curve where the performance index level corresponds to the ideal performance condition of the process.

In order to collect information in the form of a performance index level, the system injects its own test signal into the process by means of a unit 24 (FIG. 1). The test signal is preferably in the form of a step input signal and gives rise to a particular process output signal. This is fed back to the comparator 14 and compared with the input signal on line 16 to provide an error signal E applied to the self-tuning circuit 20. Step input signals are provided by a plurality of low level square wave pulses injected by unit 24 into the process at the comparator 14. The test signal need not of course be a step signal, a random signal or a sine wave for example could also serve as a test signal. The test signal can be injected continuously or in bursts to provide periodic retuning of the controller 19 as described below.

The error signal E applied to the circuit element 22 is transformed by the selected performance index block to an output signal, indicated diagrammatically in FIG. 2, which settles to a steady state voltage level 30 and is directed via a manually settable selector switch 26 to a first sample and hold element 28 which samples the level 30 and stores it. The voltage level 30 represents a performance index level X. The element 28 then passes the stored level 30 to a second sample and hold element 32 and samples and stores the voltage level generated by the selected performance index block in response to an error signal resulting from the next successive test signal. This voltage level represents a performance index level Y. The two values X and Y representing the previous and present performance index levels derived from successive test signal pulses are presented to subtracting element 34 where these values are compared to provide a difference signal. The result of a number of comparisons of successive levels might, for example, look like that illustrated diagrammatically at 36 in FIG. 2. In dependence upon the results of such comparisons which themselves depend upon the positions of the corresponding voltage levels 30 on the selected performance index curve, the signal 36 comprises a plurality of positive and negative levels each of which is the result of a comparison of two successive levels 30. A positive level indicates an increasing system error E and thus a movement of the performance index level away from the stationary or optimum value. Conversely a negative level indicates a decreasing system error and a movement of the performance index level towards the optimum. It will therefore be appreciated that when the level changes from positive to negative or vice versa this indicates that the performance index level has passed through the stationary value. The positive and negative levels are passed to a sampling device 37 which is adapted to deliver a logic "1" level for positive difference signals 36 and to deliver a logic " 0" level for negative difference signals 36. Thus, as shown diagrammatically at 38 in FIG. 2, the sampling device 37 provides a series of rectangular pulses 40 separated by spaces of width corresponding to the incidence of negative difference signals. In order to convert these pulses 40 into a more useful signal, they are passed through a divide by two element 42, such as a bistable, to provide a signal indicated diagrammatically at 44 in FIG. 2 comprising a plurality of pulses 46 whose leading edge corresponds to one of the pulses 40 and whose trailing edge corresponds to the next occurring pulse 40. Thus, the width of the pulses 46 corresponds to the spaces between the pulses 40 and hence depends upon the incidence of positive or negative differences at the subtracting element 34, this in turn being dependent upon the position of the successive voltage levels 30 on the performance index curve.

Since each change in the level of the signal 44 thus indicates that the performance index has passed through the stationary valve the signal 44 is thus in the nature of a direction control signal which can be used to govern whether the parameter which is to be optimised should be increased or decreased. This is achieved by changing the position of the zero axis of the curve 44 in a level shift device 50 to obtain positive and negative signals 52 of variable width which are passed through an integrator 54 to provide a voltage output, indicated diagrammatically at 56 in FIG. 2, of amplitude appropriate to adjust the relevant channel gain K1, K2 or K3 of the controller 19 in an increasing or reducing direction to adjust the performance index to an optimum condition.

As indicated in FIG. 2, the integrator output can be selectively passed either to adjust the channel gain K1, K2 or K3 depending upon the position of the switch 56 of a time sharing unit 58. The latter is coupled via the three channels K1, K2, K3 to the controller 19 and by means of the unit 58 each of the channel gains K1, K2 and K3 can be automatically adjusted by the circuit 20 in strict rotation by allocating a predetermined period to each in turn. The references k1, k2 and k3 are intended to refer to the manual settings of the channel gains K1, K2 and K3 which are supplemented by the automatic adjustment provided by the aforegoing arrangement, each associated manual and automatic gains being combined in a respective multiplier unit e.g. an analogue unit 60 connected to the three term controller 19.

It will be noted that a fail-safe provision is made in that in the event of a breakdown in the adaptive loop 20, the controller 19 reverts to the manual settings. A practical form of time sharing unit is shown in FIGS. 3 and 4 where the switch 56 is in the form of a shift register 70. The latter is driven by a pulse signal applied thereto from a timer 72 via a divider circuit 74, in practice a divide by 4. The integrator 54 is coupled to the amplifiers 60 by way of respective switches 76 and integrate and hold amplifiers 78 connected in series. The switches 76 may be semiconductor switches but conveniently are relays whose solenoids are controlled by the shift register 70 via further switches 80. The latter may also be semiconductor switches.

The switches 80 connect a source 82 of clock pulses to the relay solenoids such that as the shift register successively closes each switch 80 (only one switch 80 is closed at any one time) a clock pulse is applied to the associated relay solenoid to close the relay switch 76 and apply the output of the integrator 54 to the associated integrate and hold circuit 78. The latter includes a hold facility to maintain the previously received signal presented to the three term controller 19 when the associated relay switch 76 is open.

In the above manner new values for the channel gains K1, K2 and K3 are computed in strict rotation.

The clock pulses from the source 82 are also used to synchronise the operation of other circuits in the self-tuning circuit 20, for example the sample and hold elements 28 and 32 and subtracting element 34, with the time sharing unit 58.

As will be understood the time sharing technique is beneficial from a cost basis since only one adaptive loop is necessary to cover all three channel gains K1, K2 and K3 whereas a simultaneous technique would require one loop per channel gain. FIGS. 5 and 6 respectively show preferred circuits for the three term controller 19 and the performance index blocks in the circuit element 22.

Considering firstly the circuit element 22 of FIG. 5 this has an input 90 to which the error signal E is applied and a respective amplifier 92, 94, 96, 98 for each performance index function, the amplifiers having associated resistors and capacitors to provide the desired function shape. The input 90 is coupled to amplifiers 92 and 94 for the functions MSE and ISE by way of a multiplier unit 100 which multiplies the error signal E by itself to provide the required square function for MSE and ISE. The input 90 is also coupled to amplifiers 96 and 98 for the functions IAE and ITAE by way of a circuit 102 which provides a positive error signal E output regardless of the sign of the input error signal E. The time function of the ITAE function is provided by a step signal applied to input 104 of the circuit element 22 and to the amplifier 98 via an integrating amplifier 106 and a multiplier unit 108. The multiplier unit 108 multiplies the outputs signal to amplifier 98. The step signal is applied to the input 104 in synchronism with the operation of the self-tuning circuit 20.

The circuit illustrated in FIG. 6 is the practical embodiment of the system s domain transfer function which is as follows:

θ1o =K1 (1+K2 1/s+K3 S)

The circuit has an input 110 which divides into three paralleled branches each having a respective amplifier 112, 114 and 116. The outputs of amplifiers 114 and 116 are connected to respective multiplier units 118 and 120 to which the channels K2 and K3 of the self-tuning circuit 20 are also connected. The outputs of the multiplier units 118 and 120 and amplifier 112 are connected to the output of the three term controller 19 via a common amplifier 122 and a further multiplier unit 124. The channel K1 of the self-tuning circuit 20 is applied to this multiplier unit 124.

While the present invention has been particularly described with reference to three term controllers it will be obvious to those skilled in the art that the invention also applies to one or two term controllers.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3105928 *Apr 28, 1961Oct 1, 1963Sperry Rand CorpSelf-optimizing servomechanisms
US3109970 *Dec 9, 1959Nov 5, 1963North American Aviation IncSelf-adaptive servo system
US3466430 *Jan 11, 1967Sep 9, 1969Collins Radio CoExtreme parameter search control system
US3741474 *Feb 18, 1971Jun 26, 1973Tokyo Keiki KkAutopilot system
US3781626 *Dec 30, 1971Dec 25, 1973Tokyo Shibaura Electric CoOptimized p.i.d.controller
US4094959 *Feb 2, 1977Jun 13, 1978Phillips Petroleum CompanyProcess measurement and control
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4346433 *Mar 11, 1980Aug 24, 1982Phillips Petroleum CompanyProcess control
US4358821 *Jun 2, 1980Nov 9, 1982Antti NiemiMethod and apparatus for the incorporation of varying flow in the control of process quantities
US4368510 *Oct 20, 1980Jan 11, 1983Leeds & Northrup CompanyAutomatic identification system for self tuning process controller
US4385362 *Oct 20, 1980May 24, 1983Leeds & Northrup CompanyFilter arrangement for elimination of unwanted bias in a model reference process control system
US4407013 *Oct 20, 1980Sep 27, 1983Leeds & Northrup CompanySelf tuning of P-I-D controller by conversion of discrete time model identification parameters
US4451878 *Jul 14, 1981May 29, 1984Tokyo Shibaura Denki Kabushiki KaishaProcess control apparatus
US4481567 *Mar 1, 1982Nov 6, 1984The Babcock & Wilcox CompanyAdaptive process control using function blocks
US4533991 *Dec 29, 1982Aug 6, 1985Storage Technology CorporationMethod of controlling a desired parameter
US4540923 *May 14, 1984Sep 10, 1985General Motors CorporationAdaptive servomotor controller
US4563734 *Sep 13, 1983Jan 7, 1986Tokyo Shibaura Denki Kabushiki KaishaMultivariable proportional-integral-derivative process control apparatus
US4573125 *Mar 28, 1983Feb 25, 1986Messerschmitt-Boelkow-Blohm Gesellschaft Mit Beschraenkter HaftungFlight control system especially for helicopters
US4602326 *Dec 12, 1983Jul 22, 1986The Foxboro CompanyPattern-recognizing self-tuning controller
US4607326 *Feb 23, 1984Aug 19, 1986Tokyo Shibaura Denki Kabushiki KaishaSampled-data I-PD control apparatus
US4641235 *Sep 25, 1984Feb 3, 1987Kabushiki Kaisha ToshibaProcess control apparatus with process dependent switching between process control modes
US4641265 *Jul 27, 1984Feb 3, 1987Japan Tobacco Inc.System for controlling the proportion of leaf vein in tobacco raw material treating process
US4669040 *Sep 19, 1984May 26, 1987Eurotherm CorporationSelf-tuning controller
US4677542 *Jun 11, 1986Jun 30, 1987Deere & CompanySelf-tuning regulator implement control
US4719557 *May 13, 1986Jan 12, 1988Siemens AktiengesellschaftApparatus for generating a symmetrical three-phase voltage system with a neutral wire capable of carrying current
US4754391 *Sep 10, 1986Jun 28, 1988Yamatake-Honeywell Co. Ltd.Method of determining PID parameters and an automatic tuning controller using the method
US4758943 *Mar 26, 1986Jul 19, 1988Hightech Network AbMethod and an apparatus for automatically tuning a process regulator
US4791548 *Apr 18, 1986Dec 13, 1988Omron Tateisi Electronics Co.Discrete time control apparatus
US4993480 *Nov 17, 1989Feb 19, 1991Chichibu Cement Kabushiki KaishaTemperature controlling means for a thermostat for use in measuring viscosity
US5276630 *Jul 23, 1990Jan 4, 1994American Standard Inc.Of an HVAC system
US5726879 *Mar 10, 1995Mar 10, 1998Canon Kabushiki KaishaControl apparatus, a stage apparatus and a hard disk servo writer apparatus including a robust stabilizing compensator
US5742503 *Mar 25, 1996Apr 21, 1998National Science CouncilUse of saturation relay feedback in PID controller tuning
US6171066 *Jun 8, 1998Jan 9, 2001Smc Kabushiki KaishaAutomatic pneumatic pressure control apparatus and method of controlling same
US6434436 *Apr 24, 2000Aug 13, 2002Siemens AgProcess and system for setting controller parameters of a state controller
US6917840 *Dec 18, 2002Jul 12, 2005Mts Systems CorporationMethod of ascertaining control parameters for a control system
US7016743 *Jan 14, 2004Mar 21, 2006General Cybernation Group, Inc.Model-free adaptive control of quality variables
US7289735 *Apr 4, 2005Oct 30, 2007Jds Uniphase CorporationApparatus for emitting light with controllable degree of polarization
US8046091 *Apr 23, 2008Oct 25, 2011Honda Motor Co., Ltd.Control parameters for searching
USRE33267 *Jul 21, 1988Jul 17, 1990The Foxboro CompanyPattern-recognizing self-tuning controller
EP0049306A1 *Oct 30, 1980Apr 14, 1982Gebrüder Sulzer AktiengesellschaftControl circuit
EP0099131A2 *Jul 15, 1983Jan 25, 1984Phillips Petroleum CompanyGeneration of a set point for process control
EP0180669A1 *Oct 9, 1984May 14, 1986Pneumo Abex CorporationAdaptive control system
EP0190644A1 *Jan 28, 1986Aug 13, 1986Nippon Steel CorporationConvertor pressure control device in convertor waste gas disposing device
EP0203550A1 *May 23, 1986Dec 3, 1986Kollmorgen CorporationAdaptive electrical control system
EP0443737A2 *Feb 1, 1991Aug 28, 1991Kabushiki Kaisha ToshibaControl support system
WO1984002590A1 *Dec 22, 1983Jul 5, 1984Storage Technology CorpAdaptive feedforward servo system
WO1985001807A1 *Oct 14, 1983Apr 25, 1985Ford Motor CoSelective parametric self-calibrating control system
WO2002086631A1 *Apr 16, 2002Oct 31, 2002Kasai ShigeruControl method and control apparatus
Classifications
U.S. Classification700/32, 318/610, 318/561, 702/107, 700/39, 700/42
International ClassificationG05B13/02
Cooperative ClassificationG05B13/024
European ClassificationG05B13/02A2